External Forces Shaping the Earth Weathering Weathering refers to physical and chemical processes that change the characteristics of rock on or near the earth’s surface. Weathering processes create smaller and smaller pieces of rock called sediment. Mechanical Weathering Processes that break rock into smaller pieces are referred to as mechanical weathering. Agents that can break apart rocks include: running water, plant roots, ice (glaciers), and temperature. Chemical Weathering Occurs when rock is changed into a new substance as a result of interaction between elements in the air or water and the minerals in the rock. Erosion Occurs when weathered material is moved by the action of wind, water, ice, or gravity. For erosion to occur, a transporting agent, such as water or wind must be present. When a river enters the ocean, the sediment is deposited in a fan like landform called a delta. Wind Erosion Wind can also transport and eposit sediment in other locations. Loess is windblown silt and clay sediment that produces very fertile soil. Glacial Erosion A glacier is a large, long lasting mass of ice that moves because of gravity. Glaciation is the changing of landforms by slowly moving glaciers. Rocks left behind by a glacier may form a ridge called a moraine. Building Soil Organic material in the soil is called humus. Soil has parent material or the chemical composition of the rock it is made of. The relief is a factor in soil production as steeper slopes erode more quickly The organisms in the area provide material for soil. Warmer climates produce different soil. The amount of time is also a factor in soil production.